SUMMARY: Efforts will be directed towards determining the role of macrophages in controlling resistance to tolerance induction by HGG in Balb/c mice. In particular we will look for receptors for a particular subclass (IgG3) which may be present on Balb/c but not DBA/2 macrophages. We wish to determine how such a putative finding serves to inhibit tolerance induction perhaps by rapidly switching on T cells towards immunity. The nature of T cell receptors for response to the azobenzenearsonate (ABA) system will be studied in guinea pigs and rats. After developing optimal procedures for inducing ABA specific T helper and T suppressor cells, we wish to compare the two cell types in respect to kinetics, specificity and target of action. Further efforts will be directed towards a study of the antigen-presenting cell required to induced sensitized T cells to respond in the presence of ABA. We wish to test an hypothesis concerning the association of Ia molecules with ABA on the surface of antigen presenting cells.